Amid advances in optical interconnect technology, hopes are pinned on the realization of an integrated optical input-output interface that is amenable to cost reduction. As a candidate technology capable of reducing the cost of an integrated optical input-output interface, attention is focused on silicon photonics. Since silicon is an indirect gap semiconductor, the luminous efficiency of a silicon-based light emitter is low compared to the luminous efficiency of a light emitter based on an InP compound semiconductor. Thus, a light emitter that uses silicon as its active material is not preferable in terms of luminous efficiency.
An external resonator-type semiconductor laser element that hybrid-integrates an InP-based high-efficiently light emitter (semiconductor optical amplifier) on a silicon substrate is attracting attention. In this laser element, the oscillation mode is controlled by a silicon waveguide filter that is optically connected to the InP light emitter.    [Patent Document 1] Japanese Laid-open Patent Publication No. 2006-245344    [Patent Document 2] Japanese Laid-open Patent Publication No. 2009-200091